1. Gives identifiable visual feedback:
- Draws two colored lines (one vertical, one horizontal)
- Continuously blinks a pixel
2. Is interactive:
- Shifts the screen when a button is pressed, restores when released
- Changes line color when this button is an arrow button
3. Behaves consistent and doesn't crash:
- Is compatible with all ROM versions, past, present and future
- Doesn't rely on undocumented features
- Doesn't accidently clobber system variables
4. Is as small as possible
- Occupies 6 bytes of RAM (3 vCPU instructions)
- Loads at a non-intrusive memory location
Code: Select all
* file: Docs/Smallest.gt1 0207 21 0e LDW frameCount |!.| 0209 f3 17 DOKE vPC+1 |..| 020d 90 07 BRA $0209 |..| * 6 bytes * start at $0207
Believe it or not, there's actually an application for this: to provide some kind of defined behaviour in case a GT1 file is loaded on a Gigatron with an older ROM than required. You don't want it to crash when using functions that aren't present. But you still want it to behave in a manner that's identifiable. The GT1 file itself is responsible, because the Loader wouldn't know any better. So it must be as small as possible(*). A bit silly? Oh sure!
Details on the workings in the comments of Docs/Smallest.gcl.
(*) I guess it's a bit akin to the message "This program cannot be run in DOS mode" present in Windows executables. Same idea, but smaller.